Butterfly monitoring on Fleam Dyke and the Roman Road is part of a national scheme run by Butterfly Conservation. The transect method involves weekly counts along fixed routes throughout the season, under strict criteria for weather, recording area and time of day. The data collected are added up to give annual abundance indices. If a weekly count is missing, a statistical model is used to estimate the missing figure, which is included in the calculated index.
A summary of the monitoring for 2020, compiled by Roger Lemon, can be viewed here.
Butterfly counts for the years from 2007 to 2020 are shown below, courtesy of Roger Lemon: